The disclosed invention relates to a unique method and apparatus for heating calender rolls in a calender roll system where the rolls are readily changeable. The disclosed heating is particularly suitable in the method for forming tire components of predetermined cross sections.
Conventional heating methods for calender rolls include hot water steam heating and electrical resistance heating. However, with such conventional heating methods, the heating of the entire roll requires a substantial length of time.
Induction heating of rolls is also known in the art. With induction heating, heating of the roll can be both selective and rapid. Induction heaters are typically classified by the frequency of the induced current. Low-frequency heaters usually induce power frequency current in the charge. A medium-frequency induction heater induces currents of frequencies between 180 and 540 hertz while a high-frequency heater induces currents of frequencies from 1000 hertz and upwards.
U.S. Pat. No. 5,571,066 discloses heating the ends of a calendering roll. An external electromagnetic induction system heats the entire working surface of the roll while an internal electric-resistance heating system heats the roll from internally. In normal operation, only the external heating system is active. The internal heating system must be used to bring the roll up to the required operating temperature.
U.S. Pat. No. 5,123,340 discloses induction heating of softcalender and supercalender rolls. The rolls are provided with a thermally conductive coating.
U.S. Pat. No. 5,111,564 discloses two induction heating coils at the opposing ends of a roll. The induction heating compliments the hydraulic heating of the median portion of the roll.
U.S. Pat. No. 5,074,019 discloses the use of high frequency induction heating coils inside and outside of a calender roll. A number of coils are uniformly distributed the length of the entire roll. For uniform heating, a corresponding bank of induction heating coils is may be arranged along the outside length of the roll.
Almost all of the above mentioned prior art patents are concerned with increasing the roll diameter by a miniscule amount to effect a papermaking process. The prior art references fail to teach heating of a calendering roll at a separate location from the calendering process wherein at least one of the calender rolls is occasionally replaced with another roll for operation within the calendering process.
U.S. Pat. Nos. 5,513,560 and 5,762,740, both incorporated herein by reference, disclose a quick change over method and apparatus for a calendering apparatus 200. The disclosed apparatus 200 is used to form a laminate from a series of tire components, forming a tire casing. Each calender assembly 302 includes two calender rolls 350, 352, as seen in FIG. 7. The rolls 350, 352 are delivered to the assembly 302 by an overhead moveable transfer mechanism 400.
During operation of the calendering process, the calender rolls 350, 352 can be internally heated or cooled. The heating means 335 has a resistive heating element which enters through an opening in the hubs 314 or 316. The internal heating elements 335 are employed when the material being processed can be more efficiently applied in a heated environment.
While heating means are sufficient to internally heat the rolls 350, 352, greater efficiency of the calendering process is achieved when the rolls 350, 352 are heated prior to the roll delivery into the calender assembly 302.
The present invention is directed toward an improvement in the quick change over calendering apparatus. Prior to placement of the rolls 350, 352 in a calender assembly 302, the rolls 350, 352 are heated at a heating station. Heating the rolls 350, 352 prior to placement in the calender assembly 302 permits rapid start-up of the calendering operation, instead of waiting for the rolls to be heated by the formally disclosed internal heating means. The internal heating means may be used to maintain the roll temperature.
At the heating station, induction heating is the preferred method of heating. Induction heating provides almost instantaneous heating of the rolls, and is a more efficient method of heating.
This invention is an improved method of calendering a material. The material is calendered by at least one calender roll, the roll operating at a predetermined operating temperature. The calender rolls are replaced from time to time with another roll. Prior to placing the new roll into its calendering position within the calendering apparatus, the replacement roll is heated, using a heat source, from a temperature lower than the operating temperature. The preferred predetermined operating temperature ranges from 180xc2x0 to 260xc2x0 F.
The material may be calendered by a pair of associated rolls and replaced by another pair of associated rolls.
The preferred method of heating the calender rolls is by induction heating. The induction heating coil is preferably operated at a frequency range of 7 to 11 kHz.
The disclosed method of heating the calender rolls may also be used to reheat rolls which have been removed from the calendering position within the calendering apparatus.
The disclosed heating station also permits the rolls that are being heated prior to placement within the calendering apparatus, or rolls that are being reheated, to be held at any temperature for a period of time. When holding the roll for a period of time after heating the roll, the roll temperature may be constant after reaching the desired temperature or may be variable if the roll is heated to a temperature greater than the operating temperature and allowed to cool to the operating temperature during the holding period.